The specific objectives of the Clinical Research Centers are to collect data for determining sensitivity, specificity, and repeatability of ultrasound B-scan imaging relative to arteriography and to pathological findings in the detection and quantification of human atherosclerotic lesions in carotid and iliofemoral arteries and their major branches; and further, to collect data for establishing the clinical utility of ultrasound B-scan imaging as used in the detection and quantification of human atherosclerotic lesions. Each Center will be expected to recruit at least 200 patients a year for this study. Ultrasonic B-scan imaging must be directed specifically towards the study of the carotid and iliofemoral arteries and their major branches.